This invention relates to a process for purifying aluminum chloride. It particularly concerns a process for producing relatively pure aluminum chloride from ores containing significant quantities of iron as well as lesser quantities of titanium and silicon.
Bauxite presently is the principal ore from which aluminum is produced; however, bauxite is not indigenous to the United States and the countries from which the United States imports bauxite have formed a cartel for controlling and regulating the sale of bauxite. It is advantageous therefore to develop alternative methods for producing aluminum from indigenous ores not presently utilized in the United States. Particularly, clays are rich in aluminum but also contain elements such as iron, titanium and silicon, all of which are present in bauxite but exist in greater concentrations in these clay ores and must be separated in an economical and efficacious manner in order to make the recovery of aluminum from clay economically feasible.
Theoretically, chlorination of the aluminous containing material should produce various chlorides of aluminum and iron along with silicon tetrachloride and titanium tetrachloride. The various boiling points of these materials are such that selective condensation should be available to separate relatively pure aluminum chloride. Chlorination of the aluminous containing ore in the presence of carbon produces, as heretofore stated, the chlorides of aluminum, iron, silicon, and titanium and also carbon dioxide and carbon monoxide. By cooling the gaseous mixture to about 800.degree. K., ferrous chloride condenses and may be selectively removed. At about 600.degree. K. ferric chloride condenses and at about 400.degree. K. aluminum chloride condenses leaving the oxides of carbon as well as titanium tetrachloride and silicon tetrachloride. This scheme is uneconomical and not viable for two reasons. First, chlorine is an expensive reagent and an economically feasible process for recovering or winning aluminum from ores thereof requires the chlorine to be recovered for reuse in the process. The foregoing condensation reactions all result in significant losses of chlorine as iron salts as both the ferrous and ferric state condense. Secondly, iron aluminum hexachloride is formed as a complex and has about the same volatility as aluminum trichloride, whereby ferric chloride is extremely difficult to separate as a contaminate from aluminum chloride. Particularly, the ferric iron cannot be separated by selective condensation sufficiently to permit the resulting aluminum chloride to be useful as a feed material for the further processing thereof to aluminum.
For these reasons, selective condensation of the off gases from the carbo-chlorination of aluminum ores is not generally considered to be an acceptable method for the winning of aluminum metal from aluminum containing materials such as bauxite. In fact, the Bayer-Hall process is at present the only commercially used process in the United States to produce aluminum from bauxite.
The silicon and titanium, usually present in clay ores, can efficiently and economically be separated from aluminum chloride in the carbo-chlorination of aluminum ores.
The following patents relate to but do not disclose or teach the claimed subject matter of the present invention.
U.S. Pat. No. 4,083,928 issued Apr. 11, 1978 to King discloses a process for the production of aluminum chloride from coked alumina and chlorine utilizing a fluidized bed in a reaction vessel having a nitride based refractory lining.
U.S. Pat. No. 4,035,169 issued July 12, 1977 to Sebenik et al discloses a method of separating aluminum chloride from gases produced during the chlorination of bauxite, clay and other aluminous ores wherein the aluminum chloride is dissolved in a molten salt solvent to separate silicon and titanium chlorides which are insoluble and thereafter vaporizing the aluminum chloride to produce a purified liquid product.
U.S. Pat. No. 4,082,833 issued Apr. 4, 1978 to Wyndham et al discloses the use of sulfur as a reaction promoter or reaction conditioner to enhance the carbochlorination of aluminous containing materials.
U.S. Pat. No. 3,861,904 issued Jan. 21, 1975 to Othmer teaches the halogenation of aluminum with a sulfur halide followed by disproportionation of the monohalide by cooling to give aluminum metal and aluminum trihalide. Any aluminum sulfide produced in the process disclosed by Othmer is reacted with metallic iron to give aluminum and an iron sulfate which is later reduced to iron for recycling.